The present study has as its objective to understand the biosynthetic regulation and function of membrane phospholipids in Escherichia coli. Specifically, mutants in the following enzymes are being studied. a) Phosphatidylserine synthetase. The study of membrane function, especially active transport, in these organisms will have a high priority during the coming year. The uptake of antibiotics is also being examined. b) Phosphatidylglycerophosphate synthetase. New ways for isolating additional mutants in this enzyme will be sought. c) Other lipid mutants. Strains lacking diglyceride kinase have recently been isolated. They accumulate diglyceride in their membranes. The metabolic origin of this material will be determined.